There is a growing movement, driven by both industry and academia, towards a new network control paradigm called Software-Defined Networking (SDN). In the SDN paradigm, a network controller, running on one or more servers in a network, controls, maintains, and implements control logic that governs the forwarding behavior of shared network switching elements on a per user basis. A virtual network that is implemented for a tenant of a hosting system is a good example of a SDN networking. The virtual (logical) network of a tenant of the hosting system connects a set of virtual machines that are assigned to the tenant, to each other and to other virtual and/or physical networks.
One of the challenges in today's hosting system networks is extending the virtual networks (e.g., of one or more tenants) to other physical networks through physical switches (e.g., third party switches). One solution involves employing a specific type of switch to connect to the other physical networks, and having this switch serve as an L2 gateway. However, such a switch can become a bottleneck, and will have less throughput than dedicated hardware. Having the central network controller communicate directly with the third party switches requires the central controller to understand the different protocols required, and leaves the central controller subject to malicious network attacks such as Denial of Service (DoS) and Distributed DoS (DDoS) attacks from the third party switching devices.